Warning #1: an issue has been found with Tower's Pause button which can cause the vehicle to fly to an old position if the vehicle has not sent a position update to Tower in some time.

Warning #2: Copter-3.3.2 fixes a bug found in Copter-3.3.1's desired climb rate initialisation which could lead to a sudden momentary drop when switching from Stabilize or Acro to AltHold, Loiter or PosHold.

Warning #3: Copter-3.3.2 fixes an issue found in Copter-3.3.1 which could lead to hard landings in RTL or AUTO if the WPNAV_SPEED_DN was set too high (i.e. >400 or 4m/s) and/or the WPNAV_ACCEL_Z was set too low (i.e. <100 or 1m/s/s).

Warning #4: a bug was found in Copter-3.3 which could cause a sudden crash if you abort a Take-off initiated from a ground station.  Video description is here.  The bug is fixed in Copter-3.3.1 so we recommend upgrading.

Note #1: AC3.3-rc8 corrected a long standing bug in the HDOP reporting.  HDOP values will appear about 40% lower than previously but this does not actually mean the GPS position is better than before.
Note #2: if upgrading from AC3.2.1 the vehicle's accelerometer calibration needs to be done again.
Note #3: set SERIAL2_PROTOCOL to "3" and reboot the board to enable FrSky telemetry like in previous versions.
Note #4: the wiki will be updated over the next few weeks to explain how to use the new features

Copter-3.3.1 is available through the mission planner.  The full list of changes vs AC3.2.1 can be see in the ReleaseNotes and below are the most recent changes since AC3.3.

Sadly this version (and all future versions) will not run on the APM2.x boards due to CPU speed, flash and RAM restrictions.

Changes from 3.3:

1) Bug fix to prevent potential crash if Follow-Me is used after an aborted takeoff

2) compiler upgraded to 4.9.3 (runs slightly faster than 4.7.2 which was used previously)

Changes from 3.3-rc11:

1) EKF recovers from pre-arm "Compass variance" failure if compasses are consistent

Changes from 3.3-rc10:

1) PreArm "Need 3D Fix" message replaced with detailed reason from EKF

Changes from 3.3-rc9
1) EKF improvements:
    a) simpler optical flow takeoff check
2) Bug Fixes/Minor enhancements:
    a) fix INS3_USE parameter eeprom location
    b) fix SToRM32 serial protocol driver to work with recent versions
    c) increase motor pwm->thrust conversion (aka MOT_THST_EXPO) to 0.65 (was 0.50)
    d) Firmware version sent to GCS in AUTOPILOT_VERSION message
3) Safety:
    a) pre-arm check of compass variance if arming in Loiter, PosHold, Guided
    b) always check GPS before arming in Loiter (previously could be disabled if ARMING_CHECK=0)
    c) sanity check locations received from GCS for follow-me, do-set-home, do-set-ROI
    d) fix optical flow failsafe (was not always triggering LAND when optical flow failed)
    e) failsafe RTL vs LAND decision based on hardcoded 5m from home check (previously used WPNAV_RADIUS parameter)

Thanks for your testing!

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Yesterday, my copter failed during a full throttle raise.

I don't know yet why it came down, but I was in stabilize mode and it started failing during that mode, so GPS and MAG can't be the cause.

I tried to hold it by switching to loiter, but it didn't change anything.

Because of the rotation and the autopilot logging all the time, I thought it must be motor or esc failure. But the motors and escs are working fine even after the almost 60 meters falldown.

It fell into the field and one motor holder broke.

Here is a video, a picture (after the crash and with the fixed motor mounting) and the logs. I hope you can help me find the cause.


Here are the specs:

Quadrocopter 580mm

RCTimer 5010 530kv

Afro OPTO 30A ESCs

6s 5Ah 30C battery

Pixhawk flight controller (AUAV-X2)

Arducopter 3.3.1


if you are getting a lot of clipping then your vibs are too high and a lot of people are reporting it is because the bells on their motors have too much slop and removing the slop has worked wonders for them. I had the same issue on a hex with brand new motors. I've since sold off that hex and built a T960 and it no longer has the issue with the same flight controller :) Seems extreme lol but I was going to sell it anyway. The new frame and AVmount producrs nearly 0 vibs and 0 clipping.

pretty sure he said he is running DJI opto and DJI motors which means he can't run the endpoint calibrations as the DJI stock firmware doesn't support it.

No its not that. Here is a log from earlier, same copter, earlier FW. Vibes are about the same, but zero clip.

And clip doesn't go up and stay there - look at the graph you will see what I mean. Something strange going on.


Hello Dave, Have you checked your motors

Hello Dave,

I thought it could be a motor sync issue, but after taking a look at your logfile it seems that they are fine.

There is something going on with ekf. Don't know what is it. Someone more experienced with ekf would probably figure it out. I see that the ekf mag innovations are high and your vibe(x,y,z ) are very high despite the IMU vibration levels are fine.

The jello in the video confirms that is is pretty much either a vib issue or a desync issue or possibly both. Normally a spin like that means one or more of the motors went wonky. This could be an intermittent ESC issue, cold solder issue, a wiring issue, or a motor issue.  

In a desync / esc issue shouldn't the rcout channels log the failure by its attempt to raise the throttle in order to try to maintain the attitude?

I do agree so much.

I do want to make tests inside my office, and I need to override checks. I believe  that ARMING_CHECK = 0 would bypass all checks. However I could arm 3.3.1 when disabling GeoFence mode, which is a bit weird since I still have PosHod mode in flight modes...

Thanks for your answers.

I checked the motors and ESCs and they were still working fine. But I will do high load tests again today.

The copter flew perfect before the crash at this day and the day before, so I don't think sync issues could be the cause.

I am an experienced solderer and I made sure the solder joints were all perfect!

See this is the thing about "faults" is the never really go "hey, I'm about to break" Just because they worked "yesterday" doesn't mean they will work today :( And the thing about these darn desync issues is that they don't always pop up and rarely when you expect them. Intermittent problems are the hardest to diagnose. The logs "should" give you an idea where to look but I am so out of touch with all the new logging info that I would not have the 1st clue where to look. You might not even have the needed logging enabled. There are quite a few videos on desync issues and how to reproduce them so you might want to take a search on youtube.

Are you sure all of your props were tight? The only time I have seen that kind of spin on one of my hexes was when it spun a prop lose and down it came spinning like a top. The only time I have had a desync issue was on my 250 quads and they tend to just flip and crash.

But I would definitely look at your vib levels even so as they are not good and are bound to cause you issues in the future. The video showed some pretty heavy oscillations [vibes] and whilst I do not think they are what brought down your bird "this time" I would fix them before flying again.

Would it be possible to post a log with the copoter flying OK? I´m very confused about the log you posted because I can´t find the spinning in the mag or imu readings. In the log it looks like a controlled descent.

There is definitely something wrong with the sensors - in the map logging there i a sudden jump in position along with an EKF error.

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